(a) Field of the Invention
The present invention relates to a system and a method that controls warm-up of clutch fluid in a hybrid electric vehicle configured to rapidly raise temperature of clutch fluid that operates a clutch by controlling a motor while the hybrid electric vehicle is being warmed up.
(b) Description of the Related Art
Hybrid electric vehicles operate through the use of power from an internal combustion engine and power from a battery. In particular, hybrid electric vehicles are designed to efficiently combine and use power of the internal combustion engine and the motor. For example, as illustrated in FIG. 1, a hybrid electric vehicle includes: an engine 10, a motor 20, a clutch 30, a transmission 40, a differential gear unit 50, a battery 60, an integrated starter-generator (ISG) 70, and wheels 80. The clutch 30 controls power transmission between the engine 10 and the motor 20, and the ISG 70 starts the engine 10 or generates electric power by output of the engine 10.
As further shown, the hybrid electric vehicle includes: a hybrid control unit (HCU) 200 that controls the overall operation of the hybrid electric vehicle; an engine control unit (ECU) 110 that controls operation of the engine 10; a motor control unit (MCU) 120 that controls operation of the motor 20; a transmission control unit (TCU) 140 that controls operation of the transmission 40; and a battery control unit (BCU) 160 that manages and controls the battery 60.
The battery control unit 160 may also be referred to as a battery management system (BMS). In the vehicle industry, the integrated starter-generator 70 may also be referred to as a starting/generating motor or a hybrid starter & generator.
The hybrid electric vehicle may run in a driving mode, such as an electric vehicle (EV) mode using only power of the motor 20, a hybrid electric vehicle (HEV) mode using torque of the engine 10 as main power and torque of the motor 20 as auxiliary power, and a regenerative braking (RB) mode during braking or when the vehicle runs by inertia. In the RB mode, braking and inertia energy are collected through power generation of the motor 20, and the battery 60 is charged with the collected energy.
As described above, the hybrid electric vehicle uses both mechanical energy of the engine and electrical energy of a battery, uses optimal operation regions of the engine and the motor, and recovers the energy of the motor during braking, thereby increasing fuel and energy efficiency.
In the hybrid electric vehicle as described above, the clutch 30 is disposed between the engine 10 and the motor 20 instead of a torque convertor to reduce cost and to decrease torque loss. The clutch 30 is generally operated by fluid. Impacts due to engagement of the clutch 30 may affect drivability. The fluid that operates the clutch 30 is generally oil in the transmission 40. The oil filled in the transmission 40 also operates as hydraulic oil to operate the clutch 30 which is disposed within the transmission 40. In other words, the oil operates both the clutch 30 and a transmission clutch.
As illustrated in FIG. 1, the fluid flows according to the operation of an oil pump 80. The oil pump 80 is connected with the motor 20 and is operated by the motor 20. Temperature of the fluid may be detected by an oil temperature sensor 90. Since viscosity of the fluid varies based on temperature, control performance on the clutch 30 may depend on the temperature of the fluid. In particular, when ambient temperature of the fluid drops below −20 degrees Celsius, the viscosity of the fluid is significantly increased, thus causing difficulty in precise control of the clutch 30. When precise control on the clutch 30 is difficult, a substantially large shock occurs during clutch engagement, which results in deterioration of drivability.
In an exemplary embodiment of the conventional art, a control method in which the clutch slips causes the temperature of the clutch fluid to rise by frictional heat generated by the clutch slip. However, with the control method of the conventional art in which the clutch slip is used to raise the temperature of the clutch fluid, a few drawbacks associated with the clutch slip may occur.
For example, when the clutch is slipped, vibration noises may occur. In addition, since the control method of the conventional art uses the clutch slip under a substantially low temperature, durability and performance of the clutch and fuel efficiency may be deteriorated.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.